Altered Atmosphere makes one

 

what does a plenum spacer do. Fill in the answer and re-use it for your original question.

 

Sorry, the purpose of a throttle body spacer and a plenum spacer are just not the same. Plenum spacers alleviate an airflow restriction that exists above the first two intake runner inlets on the VQ35DE. The inside top of the stock plenum is very close to the top of the lower plenum runner inlets. There is only about 1/8" clearance between the first two inlets and the plenum cover. This creates a significant air flow restriction that reduces engine breathing and power output.

According to the description on e-bay, this throttle body spacer is suppose to "OPTIMIZE AIR VELOCITY, AIR PRESSURE, AIR VOLUME; MAXIMIZE AIR AND FUEL ATOMIZATION", but IMO its all BS and its not going to give you any performance gains. For one thing, there is no air-fuel mixture or atomization in the throttle body or even in the upper or lower plenums. Our engines have direct fuel injection.

My advice is to use the $70 you would spend on this POS towards a proven mod like a MD plenum spacer.

 

True. If it was that easy and cheap to get 8HP, Nissan would have done it already. Plus, the whole airflow restriction of the front 2 cylinders is also BS IMO. With today's EPA and fuel mileage standards, highly doubtful that Nissan would intentionally allow 33% of the engine displacement to run rich. If the plenum design was so restrictive, why is it also angled down on the new VQ35HR? Because of wave tuning. Flow benches don't account for valves snapping shut 20 times/second causing standing/reflected waves at the back of a manifold.

The wedge is there to minimize the amplitude of these reflections. If anything, the angle helps with cylinder stuffing of the front 2. The MD plenum spacers and other similar designs get their power from increasing the overall volume of the intake and allow for a bigger gulp of air from a lowering of pressure drop, not from fixing anything with the front 2 cylinders.

 

I never considered this line of reasoning before, but it sure sounds logical to me. I thought I remembered hearing that the reason the plenum sloped down in the front was to accomodate the strut tower bar and hood design on the 350Z engine, and it was just a design holdover on other cars with the VQ35DE, but I guess this may have been incorrect based on what you have said.
Thanks for this info.

 

If im not mistaken i believe the new plenum on the VQ is redesigned for that reason. It allows alost more air flow to the front 2 cylinders...go to motordynes website im sure they have a big right up on how it works.

-sean

 

primarily the plenum spacer is getting more air to the front runners which are slightly starved for air due to the frontward slope of the stock plenum.

The TB spacer won't do anything for this.

Edit: Ooops, didn't read DocJohn's post... same info, his is better detailed.

 

Nobody has added different explanation that the one I gave for the TB spacer. You never trust anything on ebay. Even their reasoning and justification is vague. they only othe explanation that I have found was the one on AAM's website which only adds that it comes prefabbed for boost controllers, nitrous, etc. I do beleive I'm right, and I will keep thinking this until someone can give us a better explanation. anyone?

 

you said the TB spacer does the same thing as a plenum spacer... what does this post have to do with that? My response was to the flase info of TB and plenum spacers providing same (they can't).

 

yeah, there's no way a tb spacer can provide the same gains that a plenum spacer can. All you have to do is look at the extra volume the plenum spacer provides in the plenum and look at the extra volume that the tb spacer would add. Thinking about it, it possibly could be close. I dunno, who knows?

 

Actually, if you look at the new plenum, it is angled down in the front as well. Look at the distance from the center gap between the 2 pieces in the front vs. the rear. That whole front 2 cylinder air starvation myth was started by Crawford with their flowbench "study". It had nothing to do with how an engine operates in reality. Show me a real study indicating rich ratios using a multi-channel exhaust gas analyzer in each header tube and then I'll believe it. Nissan did not angle the plenum to clear anything. If they did, then why is it angled on the new G with no strut bar?

 

I just got off the phone with Shawn Church (owner of Church Automotive Testing)… he indeed did dyno a prototype TB spacer… he confirmed that it dyno’d about 8 hp on the upper end (5500rmp range)… I asked him in theory what could possibly be the cause and he explained that the one he testing had rifling on the inside edge – you have to install it one way only… it alters the airflow in a way – unlike the Tabulator that swirls the air prior to the TB and does basically nothing, this apparently helps the airflow make the turn on our curve (from TB to plenum)… he said it did nothing on cars that have a straight intake/TB to collector.

So in theory it’s not the added volume, it the altered airflow helping the air flow around the curve after the TB.

Seems a little hokey, but I fully believe Shawn. He wouldn’t state false claims of gains. I asked about clearance (he ran a 7/8" spacer) – he has stock intake tube and said it fit but the accordion flex was collapsed all the way.

I don’t know if all manufacturers have the rifling – it looks like AAMs has functionality more for adapting other components – the rifling one might be worth looking into further. I tried doing a Google search and there are tons – so I’m not sure which one makes this particular TB spacer or if it’s even production ready… I will start researching some of the others though. Now that I know there is something other than added volume (which in theory is a bogus claim) it might be worth it?

Edit: the spacer is 7/8"... Shawn thought by recollection it was about 3/4" that's what I originally posted - after receiving the product and measuring it I have corrected the size in this post.

 

The rev-up motor addressed this issue to an extent with the lower collector - that’s why the MD MREV2(which is a modified non rev-up lower collector) and spacer works well on rev-up motors… the stock 07 may have something to the lower collector as well.

 

The TB spacer can’t add any more volume... it's not a bigger TB... The distance between the airbox and the TB is the same whether or not you use a spacer. That's why I've always wondered what the point is... but my previous post provides a little perspective (don’t know if it's entirely worth it yet).

 

I understand what you are saying, but it is just difficult for me to believe that adding some vanes or "rifling" to the inner surface of a ¾” TB spacer to produce swirling of the intake air to help it flow around the curve of the plenum can produce a 8 WHP gain. I would really like to see some verified repeatable dyno results (same day, same car, same conditons) of this TB spacer. If it worked as good as claimed I would buy one myself.